With the quickly upgraded living standards in the modern society, people pay more attention to furniture that is more convenient and practical for use. Therefore, there are diversified chairs available in the market.
Chairs that are frequently found in general families usually include integrally formed backrest and seat, and the seat usually has a fixed size. When sitting in a correct position, a person's back is rested against the backrest with two shanks naturally extended downward perpendicularly to the thighs and two heels in contact with the ground. When a child sits on a chair having a relatively large seat with his back rested against the backrest, it would be impossible for the child's two shanks to naturally extend downward perpendicularly to the thighs and two heels to contact with the ground. The child would easily get sore waist and aching back when sitting on the chair in such a position. On the other hand, when the seat has a relatively small size, an adult sit thereon with back rested against the backrest might have two legs not well supported by the seat. The adult would soon have swollen and numb shanks when sitting on the chair in such a position over a long time. Since most chairs for generally families have only one fixed size, consumers have to pay more to purchase chairs of different sizes for different family members. This would inevitably increase the family expenditure and form an economical pressure to the family.
It is therefore tried by the inventor to develop an adjustable chair backrest to overcome the problem in the conventional fixedly-sized chairs for general families.